This invention relates to orthopaedic appliances. More particularly, this invention relates to joint prostheses and especially to prosthetic devices for the replacement of metacarpal joints.
Prosthetic devices for the replacement of metacarpal joints damaged by rheumatoid arthritis, infection or trauma are well known. Typical examples of such devices are described in U.S. Pat. Nos. 3,462,765; 3,875,579; 3,681,786; 3,593,342 and 3,739,403.
While some of the foregoing prosthetic joints have attained some degree of commercial success, they have certain disadvantages. Common problems are "swan neck" deformity resulting in breakage of the prosthesis at the stem/hinge interface, tissue ingrowth in the hinge area, and bending of the prosthesis outside the joint area. Accordingly, it is an object of this invention to provide a joint prosthesis not having the foregoing disadvantages.
The joint prosthesis of this invention is an improvement over known metacarpal joint prostheses. The central portion more evenly distributes the compressive forces found in a normal metacarpal joint and due to its height being equal to or greater than its width the opportunity of "swan neck" deformity of the prosthesis is therefore reduced, as well as the incidence of breakage at the stem/hinge interface. The angled or curved slot in the central portion extending from the more distal end of the top portion in the palmar aspect volarly toward the proximal end of the bottom portion allows for proper positioning of the center of motion in the proximal and volar aspect of the hinge which conforms closely to normal anatomy, as well as creating a "ledge" which inhibits tissue ingrowth into the hinge area. The arrangement of the slot also acts as a restraint to allow bending in only one direction. The stems are also designed to reduce rotation and allow for orientation of the prosthesis.